This invention relates to pump systems for fuel injection systems.
Engine exhaust emission regulations are becoming increasingly restrictive. One way to meet emission standards is to precisely control the quantity and timing of the fuel injected into the combustion chamber to match the engine cycle. For certain engine operating conditions, effective injection rate shaping may result in reduced levels of particulates and oxides of nitrogen in the engine exhaust. One form of effective rate shaping injects fuel slower during the early phase of the combustion process, resulting in less engine noise.
Existing rate shaping techniques attempt to control injection rates by making various modifications to the injector nozzle assembly. Although these existing rate shaping techniques have been employed in many applications that have been commercially successful, there is a need for a rate shaping technique that allows more precise rate shaping than the existing modified injector nozzle assemblies.
It is, therefore, an object of the present invention to provide a pump system utilizing a high pressure restriction to precisely control quantity and timing of fuel injected into the combustion chamber of an internal combustion engine.
In carrying out the above object, a pump system for a fuel injection system is provided. The pump system comprises a body defining a high pressure pumping chamber, a plunger disposed in the pumping chamber for pressurizing fuel, a high pressure outlet, and a high pressure fluid line connecting the pumping chamber to the outlet. The system further comprises a control valve along the fluid line, and a valve and restriction arrangement along the fluid line. The control valve includes a first valve body movable between a closed position and an open position. In the closed position, pressurized fuel is routed from the pumping chamber to the outlet. In the open position, pressure relief is provided to the fluid line. The valve and restriction arrangement includes a restriction and a second valve body. The second valve body is movable between an open position and a closed position. In the open position, fuel flow from the pumping chamber is generally unrestricted by the restriction. In the closed position, fuel flow from the pumping chamber is significantly restricted by the restriction to store energy in the pumping chamber.
The pump system of the present invention advantageously utilizes a high pressure restriction to affect control over the quantity and timing of the fuel injected into the combustion chamber. In one embodiment, the body is a unit pump body, and the high pressure outlet is configured for flow communication with a fuel injector. In another embodiment, the body is a unit injector body and defines a needle chamber. An injector nozzle assembly is in flow communication with the high pressure outlet. The injector nozzle assembly includes a needle received in the needle chamber. The needle chamber receives pressurized fuel from the pump outlet. That is, embodiments of the present invention are suitable for use in both unit pumps and unit injectors.
In some embodiments, the second valve body is configured as a pressure-balance valve. In a particular application, the second valve body open position provides a flow cross-sectional area, not including any effective flow cross-sectional area of the restriction, of about two to three millimeters squared. In some embodiments, the second valve body is configured as a pressure-balanced spool valve, and utilizes a through passage as the restriction.
Depending on the particular type of control over fuel injection quantity and timing that is desired, the valve and restriction arrangement may be located between the pumping chamber and the control valve, or alternatively, the valve and restriction arrangement may be located between the control valve and the outlet. For example, a valve and restriction arrangement of the present invention between the pumping chamber and the control valve allows effective control for pilot injection, boot injection, square injection, and post injection. On the other hand, a valve and restriction arrangement located between the control valve and the outlet allows effective control over pilot operations and boot injection.
Further, in carrying out the present invention, a method of controlling a pump system for a fuel injection system is provided. The pump system has a body defining a high pressure pumping chamber, a plunger disposed in the pumping chamber for pressurizing fuel, a high pressure outlet, and a high pressure fluid line connecting the pumping chamber to the outlet. A control valve along the fluid line includes a first valve body movable between a closed position and an open position. In the closed position, pressurized fuel is routed from the pumping chamber to the outlet. In the open position, pressure relief is provided to the fluid line. The method comprises controlling a valve and restriction arrangement along the fluid line. The valve and restriction arrangement includes a restriction and a second valve body. The second valve body is movable between an open position and a closed position. In the open position, fuel flow from the pumping chamber is generally unrestricted by the restriction. In the closed position, fuel flow from the pumping chamber is significantly restricted by the restriction to store energy in the pumping chamber. The valve and restriction arrangement is controlled so as to control fuel flow from the pumping chamber to the outlet.
Advantageously, the method may be utilized to affect various types of control over the quantity and timing of the fuel injected into the combustion chamber. In an embodiment of the invention that reduces the rate of injection, the method further comprises closing the control valve for an injection by moving the first valve body to the closed position, and restricting fuel flow from the pumping chamber by moving the second valve body to the closed position to reduce an injection rate, while the control valve is closed. For a pilot injection, the method further comprises closing the control valve, restricting fuel flow from the pumping chamber while the control valve is closed, and thereafter, opening the control valve by moving the first valve body to the open position, ending the reduced rate pilot injection.
In a boot injection, the method further comprises closing the control valve for injection by moving the first valve body to the closed position, and restricting fuel flow from the pumping chamber by moving the second valve body to the closed position to reduce an injection rate and store energy in the pumping chamber, while the control valve is closed. Further, for a boot injection, the method further comprises unrestricting fuel flow from the pumping chamber by moving the second valve body to the open position to increase the injection rate, while the control valve is closed, and thereafter, opening the control valve by moving the first valve body to the open position, ending the boot injection.
For square injection, the valve and restriction arrangement is located between the pumping chamber and the control valve, and the method further comprises opening the control valve by moving the first valve body to the open position, restricting fuel flow from the pumping chamber by moving the second valve body to the closed position to store energy in the pumping chamber, while the control valve is open. The method further comprises, thereafter, closing the control valve by moving the first valve body to the closed position, and unrestricting fuel flow from the pumping chamber by moving the second valve body to the open position to increase the injection rate, while the control valve is closed.
For reducing plunger noise, the valve and restriction arrangement is located between the pumping chamber and the control valve and the method further comprises closing the control valve by moving the first valve to the closed position, and unrestricting fuel flow from the pumping chamber by moving the second valve body to the open position, while the control valve is closed. The method further comprises, thereafter, opening the control valve by moving the first valve body to the open position, and restricting fuel flow from the pumping chamber by moving the second valve body to the closed position to reduce pressure release at the plunger, while the control valve is open.
For post injection, in addition to reducing the rate of pressure release at the plunger, the method further comprises, closing the control valve by moving the first valve body to the closed position. Further, thereafter, fuel flow may be unrestricted from the pumping chamber by moving the second valve body to the open position to increase an injection rate for post injection, while the control valve is closed.
The advantages associated with embodiments of the present invention are numerous. For example, pumping systems such as unit pumps or unit injectors made in accordance with the present invention utilize a high pressure restriction to allow more precise control over the quantity and timing of injection into the combustion chamber. Embodiments of the present invention allow sophisticated control over the quantity and timing of injection and may be utilized to perform, for example, pilot operation, rate shaping including boot injection or square injection, and post injection, in addition to reducing the rate of pressure release at the plunger after an injection, to reduce noise.
Further, it is appreciated that the valve and restriction arrangement may be located between the control valve and the plunger chamber or alternatively between the control valve and the outlet depending on the particular control techniques to be performed. Boot injection may be utilized to reduce oxides of nitrogen, while square injection may be utilized during high exhaust gas recirculation rates to reduce particulates. Further, embodiments of the present invention may be utilized to perform multiple injections into the combustion chamber during a single cycle.
The above object and other objects, features, and advantages of the present invention will be readily appreciated by one of ordinary skill in the art from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.